C9.25 screws

[citivolus]

Can anyone confirm for me the thread size of the mounting holes on Celestron C9.25 OTAs? The screws that come with the scope are philips head, and I'd like to replace them with some decent hex socket screws.

The screws currently in the scope I think are #10-24 x 1/4". They measure 0.185" diameter, 24 threads per inch. I've seen people claim they are #8-32, but that just doesn't seem right.

Anyone in the know?

[Dennis]

Eric

Have a look here:

http://www.scopestuff.com/ss_c9warn.htm

It looks like 2 off 8-32 and a single 10-24.

I have some screws in the 6, 8 and 10 range if you would like to try and see what fits.

Cheers

Dennis

[g__day]

The are special guage and different froont and back. I believe they use NSF American used typically on rifle scopes - I could only find one specialist store in Paramatta that serviced Sydney.

[citivolus]

Well, that makes things fun. I wonder why they couldn't just standardise one thread for all holes... I think this is going to be some trial and error.

I think my OTA manufacture date may be a few years ago, I'll have to do some research.

Regards,
Eric

[citivolus]

Well, after a bit of checking, it appears that I have the following:

#10-24 x 1/4": All (?) front mounting holes, most back mounting holes. Total of 9.

#8-32 x 1/4": Two rear rail holes on top

#8-32 x 1/2": Finder mount


I have not pulled the three that are holding the current dovetail as I think they may be thread locked. I suspect they will be #8-32 x 1/2" in the back and #10-24 x 1/2" in the front. I'm not really concerned with swapping those ones out yet.


So I guess I need some of each of #8-32 x 1/4" and 1/2", and #10-24 x 1/4" and 1/2". I still have not figured out why they bothered with two different sizes and thread pitches.

[citivolus]

You were right about these holes. I'm betting the opposite dovetail holes are the same threads.

[citivolus]

Confirmed, both dovetail attachment points are 2x #8-32 x 1/2" back, 1x #10-24 x 1/2" front.

So the running total of screws necessary to swap out a stock configuration C9.25 OTA with dovetail attached (ignoring recessed body screws) are:

#10-24 x 1/4": 9 (assorted holes)
#10-24 x 1/2": 1 (bottom front dovetail)
#8-32 x 1/4": 2 (top rear dovetail)
#8-32 x 1/2": 4 (bottom rear dovetail, finder)
#5-40 x 1": 4 (focuser assembly cover)

Of course, I'll pick up some 1/2" versions of the 1/4" screws for the inevitable equipment attachment.

Thanks to all for the assistance.

Eric

[g__day]

That sounds right - and yes finding where you can buy 8 gauage bolts (given 10 is common) won't be simple!